The importance of genetically-engineered mice (GEM) as models of human health and disease has been unequivocally demonstrated. Because of the importance of GEM in biomedical research, the numbers of GEM lines have grown exponentially over the last five years;this astronomical growth is predicted to continue. Recognizing the scientific importance of sharing mice among investigators, the NIH developed a mouse sharing policy which states that mouse lines generated with the aid of NIH funding must be distributed and shared with the scientific community. To accomplish this goal, the NIH funded the establishment of four regional Mutant Mouse Resource and Research Centers (MMRRCs) in 1999 and 2000. This application is a competitive renewal for the Missouri/Harlan (M/H) MMRRC. Specific Aims of the proposal are: (1) To improve the efficiencies of the MMRRC service functions while continuing to provide the scientific community with a mutant mouse repository and distribution center of the highest quality. To accomplish this, we will employ state-of-the-art cryopreservationand reanimation (reestablishment of lines after cryopreservation) technologies, such as intracytoplasmicsperm injection (ICSI), nuclear transfer (NT) ovarian tissue (OT) transplantation (OTT) and injection of NT derived embryonic stem cells (ntES cells) into tetraploid embryos (ntES/4N). Using these approaches we will be able to more efficiently import, cryopreserve and reanimate lines at a cost approximately 10% of current, traditional embryo cryopreservation based approaches. (2) To conduct research aimed at increasing the value of the MMRRC. Research will include projects aimed at improving assisted reproductive technologies (ARTs) used for reanimation of mouse lines, development of biosensors for detection of pathogens and health surveillance of mutant mouse colonies, and development of new genetic and ARTs that will revolutionize the speed and efficiency with which congenic strains of mice are made. The proposed approach to the operation of the M/H MMRRC represents a new paradigm for mouse repositories. Recognizing the continued exponential growth of GEM, a new paradigm is mandatory;existing mouse resource centers simply cannot archive all of the important mouse lines using traditional methodology. Furthermore, the proposed research projects will result in even greater efficiencies for the MMRRC and the development of newtechnologies useful to the entire scientific community.